This invention relates to document handling apparatus, and more particularly to a device for preventing a document from lifting off a support deck.
In systems which involve the physical transmission of documents such as data cards, it is important that the cards be held down against the support decks across which they are transported in order to prevent jamming or improper feeding into the system equipment. Also, in some systems the card may undergo a 90.degree. change in direction, with a stop wall used to halt forward card travel and to guide the card in the new direction. In this latter type of system any hold-down device employed near the stop wall must permit the desired change in direction, yet ideally the device should also prevent the card from reversing direction by bouncing back off the stop wall.
Various hold-down devices have been employed in the prior art. For example, a bank of balls may be mounted just over the support deck, with a limited amount of vertical movement permitted for each ball. As a card is transported beneath the bank the balls prevent any significant upward card movement, and in so doing only a relatively small amount of friction is produced between the balls and the card. While this type of device is effective in holding the card down, it is fairly noisy in operation and is also somewhat expensive.
Other devices are described in various United States patents. In U.S. Pat. No. 3,070,366 to Huck et al, cards are passed under spring-biased stops which keep the cards from retreating during subsequent processing. As indicated in the drawings, the stop is a rigid member which is spring-biased at an oblique angle down against a card support deck. In U.S. Pat. No. 3,276,772 to Spika a single, very light leaf spring is used to urge the cards downward toward the seat of a punching die. The leaf spring laps over the cards and acts as a break to hold it against movement during the punching operation. In U.S. Pat. No. 3,311,370 to Hunter and No. 3,156,463 to Masterson et al, a series of resilient pusher blades are held against a support surface and moved in a reciprocating fashion to advance an underlying card by pushing against its trailing edge. While designed primarily to move the cards, the devices described in these latter two patents also perform a hold-down function.
While each of the above patents discloses a device capable of preventing cards from lifting off a support deck, they are all subject to some improvement in terms of either holding down the entire length of the card, reducing the dynamic friction acting against the card, or being adaptable for use at different locations in a document transport system.